The FieldDefinition production incorrectly passes along Yield and Await to Initializer

[rbuckton]

Per the current spec:

This passes along the Yield and Await parameters to Initializer, which seems incorrect. A class field is wrapped in an implicit function, per https://tc39.es/ecma262/#sec-runtime-semantics-classfielddefinitionevaluation, step 3.e:

So a YieldExpression and AwaitExpression should not be valid in a class initializer.

Here is an example to illustrate the issue:

async function f(p) {
  return class C {
    x = await p; // when could this possibly be awaited?
  };
}
let C = await f(Promise.resolve(1));
let obj = new C();
obj.x; // what is this value?

It seems to me that Initializer[+In, ?Yield, ?Await] should be Initializer[+In, ~Yield, ~Await].